High temperature fracturing fluids with nano-crosslinkers

ABSTRACT

A fracturing fluid system for increasing hydrocarbon production in a subterranean reservoir formation comprising a fluid composition and a base fluid, the fluid composition comprising a nano-crosslinker, and a base polymer; and the base fluid operable to suspend the fluid composition, the base fluid comprising water; wherein the fluid composition and the base fluid are combined to produce the fracturing fluid system, wherein the fracturing fluid system is operable to stimulate the subterranean reservoir formation. In certain embodiments, the nano-crosslinker is an amine-containing nano-crosslinker and the base polymer is an acrylamide-based polymer. In certain embodiments, the fracturing fluid systems comprise proppants for enhancing hydraulic fracturing stimulation in a subterranean hydrocarbon reservoir.

RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication No. 62/090,635 filed on Dec. 11, 2014 and is a continuationof U.S. patent application Ser. No. 15/830,831 filed on Dec. 4, 2017,which is a continuation of U.S. patent application Ser. No. 14/963,966filed on Dec. 9, 2015 and issued as U.S. Pat. No. 9,862,878 on Jan. 9,2018. For purposes of United States patent practice, this applicationincorporates the contents of the Provisional patent application and bothNon-Provisional patent applications by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to oil and gas well stimulation and compositionsfor the stimulation of hydrocarbon bearing oil and gas containingformations. In some embodiments, the invention relates to compositionscapable of stimulating subterranean hydrocarbon reservoirs under hightemperature and/or high pressure conditions. The compositions, incertain embodiments, comprise fracturing fluids which are crosslinkedwith nano-crosslinker and are therefore capable of transportingproppants during a hydraulic fracturing stimulation process.

BACKGROUND OF THE INVENTION

The reliable, safe and economic production of hydrocarbons is criticalto the oil and gas industry. In many instances, hydrocarbon reservestrapped within certain low permeability formations, such as certainsandstone, carbonate, and/or shale formations, exhibit little or noproduction, and may therefore be undesirable to develop. Methods such aswell stimulation may increase the permeability and hence the productionof an otherwise unproductive formation or reservoir.

During well stimulation operations, chemicals can be injected into theformation in a process known as well stimulation. Exemplary stimulationtechniques include: (1) the injection of chemicals capable of dissolvingportions of the formation and creating alternative flow paths forrecoverable hydrocarbons through, for example, acid- ormatrix-fracturing processes; and (2) the injection of water and/ornon-aqueous chemicals through the wellbore and into the formation atpressures that are sufficient to fracture the formation, therebycreating new or additional flow channels through which hydrocarbons canmore readily move from the formation into the wellbore.

In certain tight reservoirs, well productivity is typically low, thusmaking the well non-economical from a standpoint of development. Onecommonly employed technique for stimulating low productivity wells ishydraulic fracturing, which can involve the injection of fluids, such ashigh viscosity fluids, into the well at a sufficiently high rate so thatenough pressure is built up inside the wellbore to split the formationapart or form fractures. The resulting hydraulically induced fracturecan extend from the wellbore deep into the formation.

Hydraulic fracturing fluids are used extensively to enhance productivityfrom hydrocarbon reservoir formations. These fluids may be supplementedwith proppants or other compositions for inducing or increasing fractureconductivity (hereinafter “conductivity”), defined as the product offracture permeability times the fracture width for a finite conductivityfracture, in a reservoir. In the quest to produce more natural gasresources, considerable attention has been devoted to finding andextracting gas locked within tight formations with permeability in thenanodarcy to microdarcy range. The main challenges associated withworking in such formations are the intrinsically high temperature andhigh pressure bottom hole conditions. For formations with bottom holetemperatures around 350-450° F., traditional hydraulic fracturing fluidsthat use crosslinked polysaccharide gels, such as guar and itsderivatives, are not suitable because of significant polymer breakdownin this temperature range. Fracturing fluids that can work at thesetemperatures require thermally stable synthetic polymers such asacrylamide-based polymers. However, such polymers have to be employed athigh concentrations in order to suspend proppants. The high polymerconcentrations make it very difficult to completely degrade at the endof a fracturing operation. As a consequence, formation damage by polymerresidue can lower or even block formation conductivity to gas flow.

SUMMARY OF THE INVENTION

The invention relates to oil and gas well stimulation and compositionsfor the stimulation of hydrocarbon bearing oil and gas containingformations. In some embodiments, the invention relates to compositionscapable of stimulating subterranean hydrocarbon reservoirs under hightemperature and/or high pressure conditions. The compositions, incertain embodiments, comprise fracturing fluids which are crosslinkedwith amine-containing nano-crosslinkers and therefor are capable oftransporting proppants during hydraulic fracturing stimulation process.

In a first aspect of the present invention, a fracturing fluid systemfor increasing hydrocarbon production in a subterranean reservoirformation is provided. The fracturing fluid system includes a fluidcomposition and a base fluid. The fluid composition includes anano-crosslinker and a base polymer. The base fluid includes water andthe base fluid is operable to suspend the fluid composition. The fluidcomposition and the base fluid are combined to produce the fracturingfluid system. The fracturing fluid system is operable to increaseconductivity in the subterranean reservoir formation.

In certain aspects of the present invention, the fluid composition isthermally stable up to a temperature of 450° F. In certain aspects ofthe present invention, the nano-crosslinker includes a nanomaterial anda crosslinker. In certain aspects of the present invention, thenanomaterial includes a material selected from, but not limited to, thegroup consisting of silica, cellulose, carbon-based materials, andcombinations thereof. In certain aspects of the present invention, thecrosslinker includes an amine-containing crosslinker. In certain aspectsof the present invention, the base polymer includes an acrylamide-basedpolymer. In certain aspects of the present invention, the fracturingfluid system further includes a proppant selected from the groupconsisting of sand, clay, bauxite, alumina and aluminosilicates andcombinations thereof. In certain aspects of the present invention, thefracturing fluid system further includes a pH control agent selectedfrom the group consisting of potassium hydroxide, sodium hydroxide,acetic acid, potassium carbonate, sodium carbonate, potassiumbicarbonate, sodium bicarbonate, hydrochloric acid and combinationsthereof. In certain aspects of the present invention, the fracturingfluid system further includes an antioxidant selected from, but notlimited to, the group consisting of phenols, polyphenols, di-tertbutylalkyl phenols, hydroquinone, apigenin, resveratrol, ascorbic acid,tocopherol, sodium thiosulfate, sodium thiosulfate, isopropanol,methanol, ethylene glycol, thiourea, and combinations thereof. Incertain aspects of the present invention, the fracturing fluid systemfurther includes a clay stabilizer selected from, but not limited to,the group consisting of sodium chloride, potassium chloride, ammoniachloride, tetramethylammonium chloride (TMAC), other quaternarymolecules and combinations thereof. In certain aspects of the presentinvention, the fluid composition reduces the polymer loading which isrequired to stimulate the subterranean reservoir formation by at least25%. In certain aspects of the present invention, the fluid compositionreduces the polymer loading which is required to stimulate thesubterranean reservoir by at least 50%.

In a second aspect of the present invention, a method for increasingconductivity in a hydrocarbon producing subterranean reservoir formationis provided. The method includes the steps of identifying a hydrocarbonproducing subterranean reservoir formation and introducing an effectiveamount of the fracturing fluid system into the hydrocarbon producingsubterranean reservoir formation such that conductivity is increasedwithin fractures.

In certain aspects of the present invention, the fracturing fluid systemincludes a nanomaterial selected from, but is not limited to, the groupconsisting of silica, cellulose, carbon-based materials, andcombinations thereof. In certain aspects of the present invention, thefracturing fluid system is thermally stable up to a temperature of 450°F. In certain aspects of the present invention, the fracturing fluidsystem includes an amine-containing crosslinker. In certain aspects ofthe present invention, the fracturing fluid system includes a proppantselected from the group consisting of sand, clay, bauxite, alumina andaluminosilicates and combinations thereof. In certain aspects of thepresent invention, the conductivity is increased within fractures by atleast 25%. In certain aspects of the present invention, the conductivityis increased within fractures by at least 50%.

In a third aspect of the present invention, a fracturing fluid systemfor increasing hydrocarbon production in a subterranean reservoirformation is provided. The fracturing fluid system includes a fluidcomposition and a base fluid. The fluid composition includes a basepolymer and a nano-crosslinker. The base polymer includes anacrylamide-based polymer. The nano-crosslinker includes a nanomaterialand a crosslinker. The nanomaterial includes a material selected fromthe group consisting of silica, cellulose, carbon-based materials, andcombinations thereof. The crosslinker includes an amine-containingcrosslinker. The base fluid includes water.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescriptions, claims, and accompanying drawings. It is to be noted,however, that the drawings illustrate only several embodiments of theinvention and are therefore not to be considered limiting of theinvention's scope as it can admit to other equally effectiveembodiments.

FIG. 1 shows a chemical reaction scheme between polyacrylamide (PAAM)and polyethyleneimine (PEI).

FIG. 2 shows electron micrographs of non-limiting geometric shapes ofnanoparticles in accordance with some embodiments of the presentinvention. The images were recorded on a Zeiss Ultra 55 field emissionscanning electron microscope at 5 kilovolt (kV) accelerating voltagefollowing sputter coating with 5 nanometer (nm) of platinum/palladium(Pt/Pd) alloy. The micrographs were recorded at magnifications of200,000× for the spherical nanoparticles (upper image) and 125,680× forthe rod-shaped nanoparticles (lower image).

FIG. 3 shows the viscosity curve (in centipoise (cP)) at 40 s⁻¹ shearrate and 400° F. for the four fracturing fluid systems (A, B, C, and D)according to Example 1.

FIG. 4 shows a viscosity curve (in cP) at 40 s⁻¹ shear rate and 350° F.for a fracturing fluid system C according to Example 1.

FIG. 5 shows a comparison of viscosity curves (in cP) at 40 s⁻¹ and 400°F. between a 45 pptg fracturing fluid system C (with nano-crosslinker)and a 45 pptg control crosslinked fluid without nano-crosslinkeraccording to Example 1.

FIG. 6 shows a comparison of viscosity curves (in cP) at 40 s⁻¹ at 400°F. between a 45 pptg fracturing fluid system C (with nano-crosslinker)and a 60 pptg control fluid without nano-crosslinker according toExample 1.

FIG. 7 shows a comparison of the viscosity curves (in cP) at 40 s⁻¹ at400° F. for the fracturing fluid systems according to Example 2.

DETAILED DESCRIPTION OF THE INVENTION

Although the following detailed description contains specific detailsfor illustrative purposes, the skilled artisan will appreciate that manyexamples, variations and alterations to the following details are withinthe scope and spirit of the invention. Accordingly, the exemplaryembodiments of the invention described herein and provided in theappended figures are set forth without any loss of generality, andwithout undue limitations, on the claimed invention.

As used herein, the term “nanomaterial” refers to a material defined byat least one dimensional measurement up to and including 1000 nanometers(nm), alternately less than 500 nm, alternately less than 100 nm, andalternately less than 50 nm. As used herein, nanomaterial encompassesand includes nanoparticles, nanocompounds and nanofibers. For example, asphere shaped nanomaterial can have a diameter of up to 1000 nm. Forexample, a fibrous nanomaterial in the shape of cylindrical nanofibercan have a diameter of up to 1000 nm. A nanomaterial in accordance withthe present invention may comprise a crystalline material, asemicrystalline material such as a semicrystalline polymer, an amorphoussolid and combinations thereof. In some embodiments, the nanoparticle isexclusively a crystalline material. In addition, a nanoparticle for usein the present invention may assume any number of geometric shapes,including but not limited to spheres, plates, rods and discs as well asPlatonic solids such as cubes, tetrahedra, octahedra, dodecahedra andicosahedra. The use of a particular shape or geometry for a nanoparticleof the present invention may derive from a desired or expected propertyassociated with the shape or geometry. For example, compositionscomprising rod shaped nanoparticles in accordance with the presentinvention are expected to exhibit a greater relative viscosity ascompared to compositions comprising spherical nanoparticles. A fiber isconsidered to have a rod shape for the purposes of this invention. Asused herein, “rod” refers to a cylindrical shape having a diameter and aheight. Nanomaterials for use in the present invention can becommercially obtained or can be synthesized as part of the process. Itwill be understood by one of skill in the art that the nanomaterials arenot suitable for use as proppants. Without being bound to a particulartheory, it is understood that proppants require certain mechanicalproperties, such as, for example, crush strength. The nanomaterialssuitable for use in the fracturing fluid system of the present inventionare smaller in size than the proppants used in the fracturing fluidsystem of the present invention.

As used herein, a “crosslinker” refers to a compound capable ofchemically bonding to and thereby connecting (“crosslinking”) two ormore individual polymers. In certain embodiments, the crosslinker mayform one or more covalent bonds with the polymers. A crosslinker, inaccordance with the present invention, may bond to a polymer via acarbonyl, sulfhydryl, amine or imine chemical group on the crosslinker.A crosslinker for use in the present invention is not limited to anyparticular spacial arrangement and may, in certain embodiments, assumeone or more of a linear, branched or dendrimeric structure prior to orfollowing bonding to two or more individual polymers.

As used herein, a “nano-crosslinker” refers to a nanomaterial capable ofchemically bonding to and thereby connecting (“crosslinking”) two ormore individual polymers. The nano-crosslinker can be created by surfacemodification of a nanomaterial with a crosslinker. The nano-crosslinkercan be produced by pre-treating the nanoparticle with the crosslinker,whereby the crosslinker has been functionalized onto the nanoparticle.The nano-crosslinker can be a nanoparticle embedded with a crosslinker.The nano-crosslinker can be prepared by grafting a crosslinker onto ananomaterial. In certain embodiments, the crosslinker forms a coating onthe nanomaterial. Advantageously, grafting the crosslinker onto thenanomaterials extends the length of the crosslinker in ways such thatinter-crosslinking may be favored over intracrosslinking when using alarger crosslinker. Inter-crosslinking or intermolecular bonds are bondswhich exist between two different molecules. In the present invention,inter-crosslinking is favored because increased inter-crosslinkingincreases the network between the base polymer molecules and theincreased network increases the viscosity. In the fracturing fluidsystem of the present invention, the amount of crosslinker used is lessthan the base polymer so it can be more cost effective to coat thecrosslinker onto the nanomaterials instead of the base polymers onto thenanomaterials. In embodiments where the nano-crosslinker includes anamine-containing crosslinker, the nano-crosslinker can be prepared byinteracting amine-containing molecules and the nanomaterials throughionic interactions, non-covalent bonding, or covalent bonding. It willbe understood by one of skill in the art that the nano-crosslinkers ofthe present invention are not suitable for use as proppants in thefracturing fluid system of the present invention.

As used herein, the term “nanowhisker” refers to a filamentouscrystalline nanoparticle formed, for example, via acid hydrolysis,vapor-liquid-solid (VLS) growth, molecular beam epitaxy or interfacialprecipitation. In non-limiting embodiments, a nanowhisker can comprise acarbohydrate including but not limited to cellulose, a metal oxide, or acarbon allotrope including but not limited to fullerene.

As used herein, “proppant” refers to a compositional solid or gelcapable of maintaining or further inducing a hydraulic fracture in asubterranean hydrocarbon reservoir. Accordingly, solid proppants can beof uniform size and shape or may be heterogeneous or irregular in sizeand shape, for example, where compaction of the proppant is desired forreducing fracture width and resulting conductivity. Non-limitingexamples of proppants for use with the present invention includenaturally occurring and manufactured compositions such as sand and othersilica based compounds; ceramics including clay, bauxite and alumina;metal, metalloid and crystal based compositions such as those disclosedin U.S. Pat. No. 7,721,803 to Huang et al.; and resin coated proppantparticles including sand, ceramics and any other substrate capable ofserving as a proppant, where the resin may comprise one or more of anepoxy, a furan and a phenol based polymer. The proppants suitable foruse in the fracturing fluid system of the present invention are largerin size than the nanomaterials used in the fracturing fluid system ofthe present invention.

As used herein, “fluid composition” refers to a composition that isincorporated into a fracturing fluid for use in stimulating productionin a subterranean reservoir formation according to the presentinvention. The fluid composition is composed of a nano-crosslinker and abase polymer.

The present invention addresses problems associated with theintroduction of fracturing fluids and proppants into high temperaturesubterranean formations for stimulating production in a subterraneanreservoir. Embodiments of the fracturing fluid system described hereinadvantageously increase the conductivity of a subterranean reservoirfracture by reducing the polymer concentration required to fracture thereservoir as compared to other fracturing fluids. The reduced polymerload amount diminishes the volume of polymer gel residue potentiallyretained in the reservoir fractures. In addition to the operationaladvantages, including but not limited to reduced blockages/increasedconductivity and reduced difficulties in subsequent reservoir cleanupactivities, the present invention addresses potential environmental andregulatory issues associated with, for example, excessive materialdischarge and residue in a fracture fluid treated reservoir.

The compositions and methods provided herein solve several problems thatare frequently encountered during the operation of subterraneanreservoir formations, including fractures within the formations, wherehigh temperature and pressure conditions are encountered.

In certain embodiments, the compositions and methods described hereinadvantageously and unexpectedly mitigate formation damage that can becaused, for example, by a traditional fracturing gel, water blockage,and/or condensate banking. The formation damage caused by theseconditions results in reduced permeability of fluids within theformation, and subsequently leads to poor production of a well.

The present invention provides for methods and compositions capable ofstimulating hydrocarbon production in subterranean formations.

The present invention includes the fracturing fluid system forincreasing hydrocarbon production in a subterranean reservoir formation.The fracturing fluid system is produced by introducing the fluidcomposition to a base fluid and mixing the two components together. Thefracturing fluid system for use with the present invention can bedesigned based on its physicochemical properties, included but notlimited to viscosity, rheology, miscibility and thermal stability, aswell as those properties associated with the ability to carry proppantsinto fractures. The fracturing fluid system can reduce the damage in thesubterranean reservoir formation. The fracturing fluid system isthermally stable (exhibits fluid stability) at temperatures betweenabout 300° F. (148° C.) and about 450° F. (232° C.) and alternately attemperatures between about 350° F. (176° C.) and 400° F. (204° C.). Inpreferred embodiments, the fracturing fluid system is thermally stableup to a temperature of about 400° F. (204° C.). In certain embodiments,the fracturing fluid system is in an absence of components that are notthermally stable up to the temperature of 400° F., for example,polysaccharide gels, such as guar gum. The fracturing fluid system iscapable of advantageously stimulating conductivity and fractureformation in a hydrocarbon producing subterranean formation at a reducedcomponent quantity, reduced polymer quantity/concentration as comparedto presently available commercial fracturing fluids. The fracturingfluid can carry the proppant to the subterranean reservoir formation.The polymer loading of the base polymer in the fracturing fluid systemis less than 60 pptg (pounds of base polymer per thousand gallons basefluid), alternately between 20 pptg and 45 pptg and alternately between25 pptg and 40 pptg. As used herein “polymer loading” refers to thetotal weight of base polymer (in pounds) added to the base fluid as partof the fracturing fluid system. In some embodiments, the fracturingfluid system reduces the overall polymer loading required in astimulation fluid by between about 20% and about 75%, preferably by atleast about 25%, preferably by at least about 50%, preferably by betweenabout 25% and about 75%, and more preferably by between about 30 andabout 50% as compared to presently available commercial fracturingfluids. In at least embodiment of the invention, a polymer loading of 45pptg corresponds to a concentration of base polymer of 0.54 wt % in thebase fluid. It is understood by one of skill in the art thatconventional fracturing fluids include about 1 wt % of polymer andcrosslinker.

The base fluid can be any fluid capable of fracturing a subterraneanformation while suspending the fluid composition. Example fluidssuitable for use as the base fluid include aqueous fluids, non-aqueousfluids, or combinations thereof. Examples of aqueous fluids includewater, a metallic or inorganic salt solution such as brine, orcombinations thereof. Examples of non-aqueous fluids include a polarfluid such as an alcohol, a non-polar fluid such as a hydrocarbon, orcombinations thereof. Examples of alcohols include methanol and ethanol.Brines can include sodium acetate. In certain embodiments, the basefluid can include water, ethanol, sodium acetate, or combinationsthereof.

The fluid composition includes a nano-crosslinker and a base polymer.The fluid composition is a gel or gel-like substance that can besuspended in a fluid and carried into the fractures. The ratio ofnano-crosslinker to base polymer in the fluid composition can be in therange of 1:0.1 to 1:1000, alternately can be in the range from 1:1 to1:100. The crosslinking of the base polymer by the nano-crosslinker isactivated by the elevated temperatures in the subterranean reservoirformation. As used herein, the term “elevated” refers to thetemperatures in the subterranean reservoir formation being at atemperature greater than the temperature at the surface. Without beingbound to a particular theory, it is understood that a small amount, lessthan 10%, of crosslinking of the base polymer by the nano-crosslinkercan occur when the components are initially mixed, but that fullcrosslinking, greater than 90%, does not occur until the fracturingfluid system reaches a temperature between about 120° F. and about 150°F. The temperature at which full crosslinking is achieved varies basedon the chemistry of the nano-crosslinker and base polymer. In certainembodiments, the fracturing fluid system of the present invention is adelayed system.

The base polymer is any gelling agent capable of bonding to acrosslinker or nano-crosslinker and remaining thermally stable attemperatures between about 250° F. (121° C.) and about 450° F. (232°C.). The base polymer can be natural or synthetic. The base polymer caninclude acrylamide-based polymer or polyacrylamide-based polymer.Examples of acrylamide-based polymers include polyacrylamide, partiallyhydrolyzed polyacrylamide, copolymers of polyacrylamide with othermonomers, and combinations of the same.

Without being bound to a particular theory, it is believed thatnano-crosslinkers improve rheological properties of a fluid due to theirhigh surface area and high surface forces, such as electrostatic and vander Waals' forces. The nano-crosslinker can be capable of improving therheological properties of a crosslinked gel at elevated temperatures,that is temperatures between 250° F. (121° C.) and 450° F. (232° C.).The ratio of nanomaterial to crosslinker in the nano-crosslinker isbetween 1:0.01 by weight and 1:1000 by weight, alternately between 1:0.1by weight and 1:50 by weight, and alternately between 1:1 and 1:100.

The nanomaterial can be any nanocompound capable of being associatedwith the crosslinker. The nanomaterial can include inorganic materials,organic materials, or combinations thereof. Examples of inorganicmaterials suitable for use as the nanomaterial include silica. Examplesof organic materials suitable for use as the nanomaterial includecellulose and carbon-based materials. In embodiments, the nanomaterialcomprises silica, cellulose, carbon-based materials or combinationsthereof. In a preferred embodiment, silica-based nanoparticles have auniform size distribution. The top image in FIG. 2 provides SEM imagesof examples of silica-based nanoparticles. The concentration ofnanomaterials in the fluid composition can be between 0.1 ppm and 10,000ppm, alternately between 1 ppm and 1,000 ppm, alternately between 10 ppmand 200 ppm, alternately between 10 ppm and 100 ppm. In at least oneembodiment of the present invention, the concentration of nanomaterialsin the fluid composition is 72 ppm.

The crosslinker can be any chemical compound capable of crosslinking thebase polymer. In embodiments where the base polymer is anacrylamide-based polymer, the crosslinker is an amine-containingcrosslinker. Examples of amine-containing crosslinkers suitable for useas the crosslinker include amines, polyamines, copolymers of amines andother monomers, or combinations thereof. Examples of polyamines suitablefor use as the amine-containing crosslinker include polyethylenimine(PEI), spermidine, spermine, polypropylenimine, poly(N-vinylimidazole),polyamines, polyamides, polyimines and polyimides. Polyethylenimine isalso known as polyaziridine.

The fluid composition, in certain embodiments, further comprises aproppant selected from the group consisting of sand, clay, bauxite,alumina and aluminosilicates.

Additives can be included in the fracturing fluid system and can beincorporated as part of the fluid composition, can be added to the basefluid (prior to mixing with the fluid composition) or can be addeddirectly to the fracturing fluid system. The fracturing fluid system caninclude one or more of the following additives such as a pH controlagent, an antioxidant (gel stabilizer), a clay stabilizer, a breakercompound including an emulsion breaker or gel breaker, a corrosioninhibitor and a scale inhibitor.

The pH control agent can include, but is not limited to, potassiumhydroxide, sodium hydroxide, acetic acid, potassium carbonate, sodiumcarbonate, potassium bicarbonate, sodium bicarbonate, and hydrochloricacid.

The antioxidant (gel stabilizer) can be any chemical compound capable ofstabilizing the resultant polymer formed when the nano-crosslinker gelsthe base polymer. Examples of chemical compounds suitable for use as theantioxidant (gel stabilizer) can include, but are not limited to,phenols, polyphenols, di-tertbutyl alkyl phenols, hydroquinone,apigenin, resveratrol, ascorbic acid and tocopherol, sodium thiosulfate,sodium thiosulfite, isopropanol, methanol, ethylene glycol, thiourea,and combinations of the same.

Examples of chemical compounds suitable for use as the clay stabilizerinclude, but are not limited to, sodium chloride, potassium chloride,ammonia chloride, tetramethylammonium chloride (TMAC), other quaternarymolecules, and combinations of the same.

The breaker compound can be any compound capable of decomposing the basepolymer, for example when the base polymer is a polyacrylamide gel andthus reducing the viscosity of the fracturing fluid system. The breakercompound can include an emulsion breaker or a gel breaker. The breakercompound can include an oxidizer type compound. Examples of oxidizertype compounds that can be used as the breaker compound include sodiumbromate. In some embodiments, the breaker compound can be encapsulated.In at least one embodiment, the breaker compound is an encapsulatedsodium bromate. The encapsulation reduces the rate at which the gelbreaker acts to reduce the viscosity.

The fracturing fluid system of the present invention can maintain aviscosity above 500 cP (at a shear rate of 40 s⁻¹) for at least 50minutes and alternately more than 50 minutes.

The fracturing fluid system has sufficient proppant carrying viscosity(herein, “sufficient proppant carrying viscosity” means a viscositygreater than 500 cP (at a shear rate of 40 s⁻¹) for at least 50minutes), such that proppants are carried into the fracture networkwithout settling out of suspension. Advantageously, the fracturing fluidsystem, and more particularly the fluid composition leaves minimalresidue in the formation.

The fracturing fluid system is injected into the subterranean formationat pressures capable of producing fractures in the subterraneanformation.

In at least one embodiment of the present invention, thenano-crosslinker does not swell in the presence of water. In at leastone embodiment of the present invention, the crosslinking of thenano-crosslinker and the base polymer is accomplished in the absence ofa metal, metal cation, or metal complex. In at least one embodiment ofthe present invention, the nano-crosslinker is in the absence of ametal, metal cation, or metal complex. In certain embodiments of thepresent invention, the nano-crosslinker does not degrade in order tocrosslink the base polymer, such that the nano-crosslinker becomes apart of the polymer matrix. In certain embodiments of the presentinvention, the crosslinker is not released from the nanomaterial topolymerize the base polymer.

In at least one embodiment of the present invention, the fracturingfluid system includes an aqueous-based fluid, an acrylamide-basedpolymer, and an amine-containing nano-crosslinker.

In at least one embodiment of the present invention, the fracturingfluid system includes an aqueous-based fluid as the base fluid, anacrylamide-based polymer as the base polymer, an amine-containingnano-crosslinker as the nano-crosslinker, a breaker compound, a pHcontrol agent, and a clay stabilizer.

EXAMPLES

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples which follow representtechniques discovered by the inventor to function well in the practiceof the invention, and thus can be considered to constitute preferredmodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention.

The following example illustrates the viscosity of the fracturing fluidsystems produced according to the methods and compositions of thepresent invention in comparison with conventional fracturing fluids.

Example 1

Silica Nanoparticles Synthesis.

The 35 nm silica nanoparticles in accordance with the present inventionwere synthesized using a modified protocol described in Hartlen et al.(2008) Langmuir 24, 1714-1720. Generally, one example of the currentinvention includes the following experiment: 2.308 g of L-arginine (98%;Sigma-Aldrich, St. Louis, Mo.) was added to a flask containing 38.5 mLethanol (200 proof; Thermo Fisher Scientific, Waltham, Mass.) and 461.5mL ultra-pure water. The resulting solution was stirred at 150 rpm andheated from room temperature (approximately 20° C.) to 65° C. on astirring hot plate. A 31.25 mL solution of 0.3 M tetraethylorthosilicate(TEOS (98%); Sigma-Aldrich, St. Louis, Mo.) was slowly added to thesolution and stirred at 150 rpm and 65° C. for 24 hours, yielding an 18mg/mL solution of 35 nm silica-based nanoparticles.

Synthesis of Amine-Containing Nano-Crosslinker.

The crosslinker was a commercially available polyethylenimine (PEI)solution, Epomin P-1050 (MW=70,000; Aceto Corporate USA, PortWashington, N.Y.). The PEI solution was prepared by dissolving 50 gramsof Epomin P-1050 into 100 mL of 300 mM sodium acetate buffer (SigmaAldrich, St. Louis, Mo.).

A stock solution of 250 mg/ml resin content Epomin P-1050 was preparedby homogenizing 50 g of the as-received Epomin P-1050 (PEI, 70,000 MW)into 100 g of 300 mM acetate buffer. Into this solution, the 35 nmsilica-based nanoparticles suspension was added in 125 aliquots, each of400 microliter (μL), in one minute intervals. At the completion of theaddition, the suspense was collected and cleaned via diafiltration on across-flow filtration device by a KrosFlo® Research IIi Tangential FlowFiltration System with a 750 kD polyethersulfone (PES) membrane. Thisresulted in an amine-containing nano-crosslinker. The concentration ofnanoparticles in the amine-containing nano-crosslinker was 9 mg/mL,while the concentration of Epomin P-1050 coating was determined, usingthermogravimetric analysis (TGA), to be four times the weight of the(uncoated) silica nanoparticles for a concentration of 36 mg/mLcrosslinker in the amine-containing nano-crosslinker.

General Procedure to Make Fracturing Fluid Systems.

The base polymer was a commercially available synthetic polymer capableof performing as a viscosifying/suspension agent at elevatedtemperatures, hydrated HE® 100 (Chevron Phillips Chemical Company, TheWoodlands, Tex.). The fracturing fluid was water. Fluid samples wereprepared using a Waring blender. For example, a 45 pounds per thousandgallons (pptg) base gel was prepared by hydrating 5.4 grams of HE® 100dissolved in 1 liter of tap water. Additional additives such as pHcontrol and antioxidant were added to the base polymer solution followedby different amounts of the nano-crosslinker according to Table 1.produced by mixing the amine-containing nano-crosslinker at aconcentration of 5 gallons of nano-crosslinker per thousand gallons ofbase fluid (gpt) of with a solution of to produce a 45 pounds perthousand gallons (pptg) fracturing fluid system.

Table 1 details the fracturing fluid systems produced and tested inExample 1.

Fracturing Concentration of Base Polymer Fluid System Nano-crosslinkerConcentration A 5 gpt 45 pptg B 7 gpt 45 pptg C 8 gpt 45 pptg D 10 gpt45 pptg

Physicochemical Measurements and Performance of Fracturing Fluid System.

To measure the viscosity of each of the fracturing fluid systems underreaction conditions designed to simulate those in a high temperature andhigh pressure subterranean reservoir formation, 52 mL aliquots of eachfracturing fluid system were injected into a Grace M5600 HPHT rheometerequipped with a B5 bob configuration. Under the reaction conditions, thenano-crosslinker reacts with the base polymer and increases theviscosity of the fracturing fluid system. FIG. 3 shows the viscositycurves produced by fracturing fluid system A, fracturing fluid system B,fracturing fluid system C, and fracturing fluid system D at a shear rateof 40 s⁻¹ and a temperature of 400° F. FIG. 4 shows the viscosity curveproduced by fracturing fluid system C at a shear rate of 40 s⁻¹ and atemperature of 350° F. According to FIG. 4, the viscosity is at least1800 cP for greater than 120 minutes at 350° F. FIG. 5 shows thecomparison of viscosity curves (in (cp)) at 40 s⁻¹ between the 45 pptgcrosslinked fracturing fluid system C and a control 45 pptg fluid withEpomin P-1050 only (without nanoparticles; same amount of Epomin P-1050as fracturing fluid system C with the nano-crosslinker) at 400° F. Ascan be seen in FIG. 5, the viscosity performance of fracturing fluidsystem C is better than the control fluid without nano-crosslinker, thatis the viscosity of fracturing fluid system C stays above 500 cP for alonger period of time. These results were compared to literature valuesfor commercially available, high temperature fracturing fluids injectedto a fracture at concentrations of 66 pounds per thousand (ppt) and 88ppt as described in Funkhouser et al. 2010. Hydraulic Fracturing UnderExtreme HPHT Conditions: Successful Application of a New Synthetic Fluidin South Texas Gas Wells. Paper SPE132173 presented at the Society ofPlastic Engineers Deep Gas Conference and Exhibition, Manama, Bahrain,24-26 Jan. 2010 (hereinafter “Funkhouser”). The concentration valueswere obtained using the published value provided in FIG. 2 of Funkhouserfor the 66 ppt fluid (with a high temperature polymer mass/volumepercentage of 0.79%), while the 88 ppt value results from themathematical product of the 66 ppt fluid concentration and the fluidpolymer mass/volume percentage ratio, i.e. (66 ppt*(1.05%/0.79%)). Whencompared to the fluids in Funkhouser, it was noted that the presentinvention exhibited thermal stability at 400° F. while advantageouslyrequiring approximately 30-50% less fluid for fracture treatment.

As shown in FIG. 6, the fluid viscosity of fracturing fluid system C wascompared to a fluid containing the same amount of Epomin P-1050, butwithout nanoparticles, for a 60 pptg HE®100 fluid. The fracturing fluidsystem C exhibited comparable viscosity at a 25% polymer loadingreduction and a resulting decreased fluid composition volume requiredfor fracture treatment.

Example 2

Synthesis, Physicochemical Measurements and Performance of NanowhiskerBased Nanofluid Solution Compositions.

Cellulose nanowhiskers were oxidized based upon a modified protocoldescribed in Dash et al., Cellulose 19, 2069 (2012). Briefly, an aqueousdispersion of cellulose nanowhiskers (250 mL, 2 wt % m/v) was sonicatedon a ⅛″ diameter microtip sonicator for 30 minutes employing a pulseduration of 2 seconds followed by a delay of 2 seconds at an amplitudeof 30%. After cooling to room temperature, 0.6 grams (2.80 mmols) ofsodium periodate was added to the suspension under magnetic stirring.The reaction was covered with aluminum foil (to prevent photolysis) andstirred at room temperature for approximately 48 hours.

The resulting suspension was dialyzed against 3 liters of deionizedwater using a 10,000 Dalton molecular weight cut-off (MWCO) dialysismembrane with frequent exchanges of dialysate for approximately 72hours. For grafting Epomin P-1050 onto the oxidized cellulosenanowhiskers, an appropriate amount of Epomin P-1050 dispersed in 200 mLof acetic acid/acetate buffer (pH 4.5) was added to a round bottomflask. A 50 mL drop-wise addition funnel was attached to the roundbottom flask for mixing with the oxidized nanowhisker suspension. Thenanowhisker solution was added to the Epomin P-1050 at a rate ofapproximately 1 mL/min with rapid magnetic stirring. The reaction wasallowed to proceed for approximately 6 hours before the addition of anexcess of NaBH4 (2-fold mass excess relative to Epomin P-1050). Thereaction was stirred overnight prior to neutralization using 1 molarhydrochloric acid (aqueous). After neutralization, the crude mixture waspurified via diafiltration on a cross-flow filtration device.

Fracturing fluid systems comprising 45 pptg HE®100 crosslinked withdifferent concentrations of Epomin P-1050 coated nanowhiskers wereproduced. The nanowhisker concentration in each fracturing fluid systemwas 4.6 mg/mL. The Epomin P-1050 concentration in each fracturing fluidsystem was 25 mg/mL.

Table 2 details the fracturing fluid systems produced and tested inExample 2.

Fracturing Concentration of Base Polymer Fluid System Nano-crosslinkerConcentration E 5 gpt 45 pptg F 10 gpt 45 pptg G 20 gpt 45 pptg H 30 gpt45 pptg I 35 gpt 45 pptg

Fracturing fluid systems were produced according to Table 2 andevaluated in a Grace M5600 HPHT rheometer equipped with a B5 bobconfiguration. The viscosity curves at 40 s⁻¹ shear rate and 400° F. foreach fracturing fluid system of Example 2 are shown in FIG. 7.

Based on the viscosity curves, it was determined that the fracturingfluid system G comprising 20 gpt of nanowhisker type nano-crosslinkerexhibited the best viscosity and thermal characteristics, that is theviscosity of fracturing fluid system G is greater than 500 cP for alonger period of time than any other fracturing fluid tested.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions, and alterations canbe made hereupon without departing from the principle and scope of theinvention. Accordingly, the scope of the present invention should bedetermined by the following claims and their appropriate legalequivalents.

The singular forms “a”, “an” and “the” include plural references, unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently describedcomponent may or may not be present or the event or circumstances may ormay not occur. The description includes instances where the component ispresent and instances where it is not present, and instances where theevent or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

Throughout this application, where patents or publications arereferenced, the disclosures of these references in their entireties areintended to be incorporated by reference into this application, in orderto more fully describe the state of the art to which the inventionpertains, except when these references contradict the statements madeherein.

What is claimed is:
 1. A fracturing fluid system for increasinghydrocarbon production in a subterranean reservoir formation, thefracturing fluid system comprising: a fluid composition, the fluidcomposition comprising: a base polymer, wherein the base polymercomprises an acrylamide-based polymer, and a nano-crosslinker, thenano-crosslinker comprising: a nanomaterial, wherein the nanomaterialcomprises a material selected from the group consisting of silica,cellulose, carbon-based materials and combinations thereof, and acrosslinker, wherein the crosslinker comprises a chemical group selectedfrom the group consisting of carbonyl, sulfhydryl, amine and imine;wherein the nano-crosslinker is produced by a method selected from thegroup consisting of pre-treating the nanomaterial with the crosslinkersuch that the crosslinker has been functionalized onto the nanomaterial,embedding the crosslinker on the nanoparticle, grafting the crosslinkeronto the nanomaterial, and coating the crosslinker on the nanomaterial,a base fluid, wherein the base fluid comprises water.
 2. The fracturingfluid system of claim 1, wherein the base polymer is operable tochemically bond to the crosslinker of the nano-crosslinker to form anetwork.
 3. The fracturing fluid system of claim 1, wherein thefracturing fluid system is thermally stable up to a temperature of 450°F.
 4. The fracturing fluid system of claim 1, further comprising aproppant selected from the group consisting of sand, clay, bauxite,alumina and aluminosilicates and combinations thereof.
 5. The fracturingfluid system of claim 1, further comprising a pH control agent selectedfrom the group consisting of potassium hydroxide, sodium hydroxide,acetic acid, potassium carbonate, sodium carbonate, potassiumbicarbonate, sodium bicarbonate, hydrochloric acid and combinationsthereof.
 6. The fracturing fluid system of claim 1, further comprisingan antioxidant selected from the group consisting of phenols,polyphenols, di-tertbutyl alkyl phenols, hydroquinone, apigenin,resveratrol, ascorbic acid and tocopherol, sodium thiosulfate, sodiumthiosulfite, isopropanol, methanol, ethylene glycol, thiourea andcombinations thereof.
 7. The fracturing fluid system of claim 1, furthercomprising a clay stabilizer selected from the group consisting ofsodium chloride, potassium chloride, ammonia chloride,tetramethylammonium chloride (TMAC), other quaternary molecules, andcombinations thereof.
 8. The fracturing fluid system of claim 1, whereinthe fluid composition reduces a polymer loading required to stimulatethe subterranean reservoir formation in a hydraulic fracturing processby at least 25%.
 9. The fracturing fluid system of claim 1, wherein thefluid composition reduces a polymer loading required to stimulate thesubterranean reservoir formation in a hydraulic fracturing process by atleast 50%.